1. Field of the Invention
The present invention relates to an LED chip and an LED array chip, and also relates to an LED array head for use as a recording light emitting element for forming a permanent visual image on a recording material by an electrophotographic recording system and an LED array chip disposed on the head. Moreover, the present invention relates to an image-forming apparatus provided with an LED array head.
2. Related Background Art
A conventional self-scan LED array (hereinafter referred to as xe2x80x9cSLEDxe2x80x9d) is disclosed in Japanese Patent Application Laid-open Nos. 1-238962, 2-208067, 2-212170, 3-20457, 3-194978, 4-5872, 4-23367, 4-296579, and 5-84971, Japan Hard Copy ""91 (A-17) xe2x80x9cProposal of Light Emitting Element Array for Optical Printer with integrated Drive Circuitxe2x80x9d and the Society of Electronic Information Communication (""91. 3.5) xe2x80x9cSelf-scan Light Emitting Element (SLED) using PNPN Thyristor Structurexe2x80x9d, and the like, and has been noted as a recording light emitting element. An LSI chipped self-scan LED array is hereinafter referred to simply as an LED array chip.
Here, an SLED array head constitution will be described. For the head, a schematic view is shown in FIG. 12. Numeral 211 denotes an SLED semiconductor chip (LED array chip), and 212 denotes a base substrate with the SLED semiconductor chip mounted thereon, in which a printed wiring board of a glass epoxy material, a ceramic material, or the like is used. Numeral 213 denotes a connector for receiving a control signal, and a power source from the outside. Numeral 214 denotes a lighting control circuit (driver IC) for generating a lighting control signal of the SLED semiconductor chip.
Numeral 215 denotes a bonding for connecting output signals xcfx861, xcfx862, xcfx86S, xcfx86I from the driver IC and a negative electrode side power source input (GND in the present example) to the respective SLED semiconductor chips, 216 denotes a positive electrode side power source pattern (+5 V in the present example) drawn to the base substrate 212, and 217 denotes a silver paste for establishing an electric conduction between the positive electrode side power source pattern 216 drawn to the base substrate 212 and a back surface electrode of the SLED semiconductor chip 211 and for bonding/fixing the chip.
Referring to FIG. 13, in order to radiate light 222 emitted from a light emitting portion 221 of the LED array chip 211 to a light-sensitive drum 224 without any loss, air and a condensing rod lens array 223 are usually present on a light path of the LED array chip 211 mounted on the substrate 212. The surface of the LED array chip 211 is usually provided with a pattern wiring 231 by aluminum. When the aluminum wiring 231 is exposed to the surface, however, aluminum is corroded by humidity, impurities, and the like in the air, and resistance value increase and wire breaking defect are sometimes caused in a short period. Therefore, in a conventional art, a polyimide or another resin film 232 functioning as a light transmission protective film is formed on the chip surface, so that the aluminum wiring 231 is prevented from being exposed.
However, since it is difficult to form the resin film 232 in a uniform and thin film thickness on the chip surface, a quantity of light emitted from the LED light emitting portion 221 and passed through the resin film 232, and light quantity unevenness among light emitting pixels are remarkably adversely affected. Moreover, for this purpose, particularly when a special semiconductor thin film forming process is added to form the resin film 232, considerable equipment investment is necessary, and manufacture cost of the LED array chip largely increases.
Moreover, as shown in FIG. 13, when the surface protective resin film 232 with a thickness longer than a light emitting wavelength is added, multi-reflection remarkably occurs in the surface protective film, and therefore flare light mixed from portions other than the light emitting portion deteriorates LED array optical properties.
An object of the present invention is to provide an LED array chip which can minimize LED optical property deterioration by addition of a surface protective film, and mainly side effects such as light quantity drop and light quantity dispersion increase among light emitting bits, an LED array head provided with the LED array chip, and an image-forming apparatus provided with the LED array chip.
According to the present invention, there is provided an LED array chip comprising a plurality of LED light emitting elements arrayed in a row, in which a surface insulating film formed by using the same material as a material of an inner-layer insulating film for forming a window to connect a wiring pattern in an internal electric circuit constitution and for establishing electric insulation between circuits and by using the same thin film forming process as a process of the inner-layer insulating film, and is formed on the entire surface of a final surface layer excluding a wire bonding pad and including a light emitting portion surface in a film thickness shorter than any light emitting wavelength of the plurality of LED light emitting elements.
Moreover, in the aforementioned LED array chip of the present invention, for the thickness of the surface insulating film, a center value is not more than 0.5 xcexcm and not less than 0.1 xcexcm.
Furthermore, in the aforementioned LED array chip of the present invention, the materials of the inner-layer insulating film and the surface insulating film are SiO2.
Additionally, in the aforementioned LED array chip of the present invention, the thickness of the inner-layer insulating film is not less than once and not more than twice the thickness of the surface insulating film.
Moreover, in the aforementioned LED array chip of the present invention, a pattern wiring is disposed between the inner-layer insulating film and the surface insulating film.
According to the present invention, there is provided an LED array head comprising the aforementioned LED array chip.
According to the present invention, there is provided an image-forming apparatus comprising the aforementioned LED array head.
According to the present invention, there is further provided an LED chip comprising a substrate, a light emitting portion comprising an LED, and a driving portion for driving light emission of the light emitting portion, in which the light emitting portion and the driving portion are disposed on the same surface of the substrate, a surface protective layer for covering the light emitting portion also covers the driving portion, and a thickness of the surface protective layer is shorter than a wavelength of light emitted by the light emitting portion.